Experiments will develop a battery of test for four different classes of biomarkers of aging: Sensory and motor function, learning and memory, reproductive function, neuroendocrine function. For each biomarker, two strains of mice and two strains of rats will be tested in a series of preliminary experiments designed to establish the most effective task parameters to detect age-related changes in the biomarker at different chronological ages. The performance of diet-restricted and ad libitum fed animals will assess the effects of this manipulation, which increases longevity, on behavioral and physiological functions. The data analysis will provide measures of reliability and validity, and assess different theoretical descriptions of aging of processes. The most reliable and valid procedures will be combined into a test battery that can be administered to an animal to assess the four classes of biomarkers. A cross-sectional between-subjects design will assess the interrelationship of the different biomarkers, and a longitudinal, within-subjects design will assess the predictability of the biomarker profile at one age for the profile at a subsequent age, and the interrelationship between the rates of change in the different biomarkers.